New clue to mystery illness / Nasty strain of common cold virus may be culprit

Sabin Russell, Chronicle Medical Writer

Published 4:00 am, Tuesday, March 25, 2003

American scientists suspect that a new and nasty strain of a common cold virus is responsible for a deadly outbreak of a flulike illness from China.

Researchers at the federal Centers for Disease Control and Prevention in Atlanta spotted the potential culprit -- a previously unknown member of the coronavirus family -- during a weekend of testing of samples shipped to the United States from Hanoi, Hong Kong and Singapore.

Health officials say it is responsible for killing 17 people and sickening hundreds of travelers and health care workers throughout the world.

The weekend discovery sets the stage for a scientific face-off with researchers in Asia and Europe, who believed that the cause is a different virus, from a family related to measles and mumps.

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'LEADING HYPOTHESIS'

At an Atlanta news conference, CDC director Dr. Julie Gerberding said that "the leading hypothesis" was that a virulent new form of the virus was the cause of the outbreak. "It is not identical to the coronaviruses that we've seen in the past, so this may very well be a new or emerging coronavirus infection," she said.

Gerberding said genetic material from the suspected virus had been sent Saturday to a laboratory at UC San Francisco, which used a new technology that screens for viral genes and can match a sample within a day. The UCSF screen compared the genetic code from the sample with more than 1,000 known viruses and found that it was indeed a coronavirus, but different from known strains of it. The results were sent to the CDC prior to Monday's announcement.

The family of coronaviruses causes common colds that are highly contagious but seldom lead to serious illness. This one may be a potentially lethal exception.

Worldwide, the illness that had been labeled SARS, or Severe Acute Respiratory Syndrome, has sickened 456 and killed 17, according to the World Health Organization.

QUARANTINE IN SINGAPORE

In Singapore, health authorities on Monday ordered 724 people thought to have been exposed to the disease to stay home for 10 days, the predicted incubation period of the illness.

There are 39 suspected cases in the United States, but no deaths. Officials believe 32 of the 39 are people who had traveled to Asia, and the other seven caught it from the travelers.

Many of the American cases are of patients who already have recovered from their illnesses -- a fever and a breathing difficulties that can lead to pneumonia.

Two new California cases have been added to the list, bringing the state's total to 10. One is of a 37-year-old Santa Clara County woman who was hospitalized Saturday. She was traveling in Asia with a 38-year-old man who was hospitalized on March 17 and is now listed in good condition. The woman is listed in fair condition, according to Santa Clara County Health Department spokesman Mark Schenone.

There are now three Santa Clara County residents on the list, including a man released from a Denver hospital. Also among the state cases are a father and son in Los Angeles County who have recovered; two members of a Placer County household who had mild illnesses; and single cases in Riverside, Alameda and Sonoma counties.

Alameda County spokeswoman Sherry Willis said the person suspected of being infected there had been hospitalized but had recovered and been released.

DISTINCTIVE 'CROWN'

The coronavirus family draws its name from the distinctive "crown" of spikes and globular proteins that surrounds each virus particle. Scientists at the CDC have used powerful electron microscopes to photograph these particles in samples taken from patients' lung and kidney tissue.

The CDC's leading suspect is an entirely different virus from microbes that laboratories in Hong Kong, Germany, Singapore and Canada appeared to be cornering last week. The initial suspect was an unknown strain of paramyxovirus, a large viral family that includes measles, mumps and respiratory syncytial virus -- a common winter bronchial infection known as

RSV.

Joseph DeRisi, the UCSF biochemist whose lab was tapped by the CDC, has developed a microarray test consisting of 12,000 tiny pools on a slide that are probed for specific genetic signatures of viruses. "We've built a microarray that contains every known, completely sequenced virus," he said. "If it's a virus, and it's been sequenced, we have it."

In addition, the test can spot previously unknown viruses if they share traits with known viral families and can also determine whether multiple viruses are present in a sample.

"If we get the virus family, it can be the first step in identifying a novel virus," DeRisi said.

Gerberding described the UCSF test as "the absolute state-of-the-art probe for viral genes."

The CDC also is collaborating with the Department of Defense, which is running a battery of tests to see whether the suspect virus is susceptible to any known anti-viral drugs.

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